Researchers improve energy efficiency and lifetime of LECs

Organic light-emitting electrochemical cells (LECs) have been produced using a roll-to-roll-compatible process under ambient conditions.

‘LECs can thus be produced as inexpensive and large-area, extremely thin, light-emitting devices for informative displays and, at a later stage, lighting applications,’ said Ludvig Edman, a professor of physics at Umeå University in Sweden.

Edman’s university group is focusing on novel organic compounds (such as light-emitting and conducting polymers and graphene) and developing LECs based on such materials.

The researchers are said to have improved the energy efficiency and lifetime of LECs, as well as demonstrated the unique physics and chemistry behind their operation and have recently enhanced the performance of LECs to a point where lifetime and efficiency make them useful for signage applications.

According to a statement, the next step in the development was to ensure that the manufacturing costs were attractive for commercial applications.

Using air-stable materials in a roll-coater apparatus, the team managed to deposit a light-emitting layer and a PEDOT-PSS anode on top of a flexible cathode-coated substrate mounted on a roll by means of a slot-die head.

The layers in the produced LEC device were found to be highly uneven, and the layer thickness — for the active layer and anode — was very thick at approximately 1µm.

However, due to the self-doping operation of the LEC, the light emitted did not suffer from the rough interfaces and was found to be very uniform. This feature is reportedly ideal for roll-to-roll processes, as the demands of the coating quality can be relaxed, thereby lowering costs.

All the steps involved — including preparation of inks, the subsequent coating of the constituent layers and the final device operation — could be executed under ambient air.

The experiments were carried out in collaboration with Prof Frederik Krebs and Henrik Dam at the Technical University of Denmark.

‘It was great to work with Frederik Krebs’ group so that we could quickly prove that our 10×10 cm² application techniques for LECs were transferrable to roll-to-roll processing,’ said Andreas Sandström, a PhD student at Umeå University.